Remove unnecessary echo uses from examples (#7500)

`echo` tends to confuse new Nu users; they expect it to work like
`print` when it just passes a value to the next stage of the pipeline.

We haven't quite figured out what to do about `echo` in the long run,
but I think a good start is to remove `echo` from command examples where
it would be unnecessary and arguably unidiomatic.

crates/nu-command/src/strings/format/command.rs

@@ -78,7 +78,7 @@ impl Command for Format {
             },
             Example {
                 description: "Print elements from some columns of a table",
-                example: "echo [[col1, col2]; [v1, v2] [v3, v4]] | format '{col2}'",
+                example: "[[col1, col2]; [v1, v2] [v3, v4]] | format '{col2}'",
                 result: Some(Value::List {
                     vals: vec![Value::test_string("v2"), Value::test_string("v4")],
                     span: Span::test_data(),